Zirconia has a monoclinic ambient phase with several important phases formed under extreme conditions. TaON is an oxynitride material displaying similar characteristics to $\mathrm{Zr}{\mathrm{O}}_2$ in that it also has an ambient monoclinic phase. A theoretical study is carried out using the local density functional theory to investigate the properties of similar structural phases as those displayed in $\mathrm{Zr}{\mathrm{O}}_2$ for the system TaON. The intermediate structure $\mathrm{Zr}\mathrm{Ta}{\mathrm{O}}_3\mathrm{N}$ is also investigated and the stability of these materials related to the parent phases $\mathrm{Zr}{\mathrm{O}}_2$ and TaON. Smooth trends are observed between $\mathrm{Zr}{\mathrm{O}}_2$ and TaON in the electronic properties with a steady change in compressibility. The elastic constants of high-pressure phases are also obtained strongly implying that the hardness increases between $\mathrm{Zr}{\mathrm{O}}_2$ and TaON.

• Received 17 October 2005

DOI:https://doi.org/10.1103/PhysRevB.73.134110